Shower pan/drain install

After removing old shower pan and liner I was left with 1 1/2" PVC coming out of 2" PVC. The 1 1/2" is quite flimsy. The 1 1/2" only goes into 2" only to about 6" down. Look at attached picture. Not sure exactly what to do at this point. Can I just pull this 1 1/2" out and use the 2"? It seems as though a slight tug would pull it out. Why would it be plumbed this way to begin with? Totally lost here...any suggestions would help. The shower pan and liner were done completely wrong and I'm pretty sure that this is another example of this. Thanks.

Shower pan/drain install

Thanks for the help. I pulled the 5" piece of 1.5" out and plumbed new drain to the 2". It looked to me like the previous contractor or owner siliconed in a piece of 1.5" into 2" because they were too lazy to chip a little bit of cement to plumb with 2". Which would explain why the shower pan was so thick!